C. elegans is a premier model organism for studying basic questions in development biology of general relevance to human development and disease. The overall goal of this grant is to investigate spatial, temporal and environmental regulation of early gonadogenesis in C. elegans. The somatic gonad of C. elegans is an experimentally tractable model for studying mechanisms and signaling events underlying organogenesis. We will use powerful methods for genetic analysis, live imaging, molecular manipulation and genome engineering to achieve three specific aims. Two of the aims are concerned with spatial patterning involving Notch-mediated cell-cell interactions in early gonadogenesis. We will study how stochastic processes generate differences between developmentally equivalent cells that are resolved by LIN-12/Notch signaling, and how an asymmetry in the requirement for Notch signaling is generated and contributes to cell fate diversification. The basic biology of these aims is highly relevant to understanding the cellular dynamics underlying stem cells, organismal development, and the maintenance of tissue homeostasis in vivo; cell fate reprogramming with potential therapeutic applications ex vivo; and cancer biology. What we learn about Notch signaling and mechanisms to diversify cell fate will be directly applicable to other contexts in normal development and, since aberrant Notch activity has been implicated in many different cancers and in developmental, immune, and neurological disorders, the proposed work has many implications for human health and disease. We will also investigate how temporal progression of cellular and morphogenetic events during gonadogenesis is controlled under different environmental conditions. In particular, we will study the regulation of cellular quiescence, a state in which cells have exited the cell cycle but remain capable of re- entering it, in early gonadogenesis. Quiescence is a fundamental cellular property that allows stem cells to persist over time without losing developmental potential. In the third aim, we will study how temporal and environmental information controls the entry into and emergence from quiescence of gonadal blast cells. Environmental regulation of developmental progression utilizes a highly conserved insulin signaling pathway, so studying how the environment impacts early gonadogenesis is potentially relevant to prevalent human diseases including diabetes and obesity. In sum, the proposed work has many implications for basic human developmental biology and for human health and disease. The deeper understanding of developmental mechanism we will achieve through these studies will be potentially applicable for developing diagnostic and therapeutic tools for human disease, a central mission of the NIH.